In quantum information we use quantum mechanical systems (qubits) instead of classical bits to store information and run algorithms. We can then utilize quantum phenomena such as superposition and entanglement in data processing. The problem when applying this technology is noise from the environment. When a qubit is affected by other systems in the environment it loses the special quantum information. This process is called decoherence. We study the decoherence of a qubit coupled to a two-level system in the environment, asking when the two-level system can be approximated as a source of classical telegraph noise.